The major objective of this research proposal is to evaluate by which mechanism(s) pretreatment of the female rat with ethynyl estradiol alters the response of the liver to glucagon. We will investigate how the actions of glucagon, which oppose those of estrogen, are modified by pretreatment of the animals with ethynyl estradiol. Investigations of the interaction of glucagon and ethynyl estradiol in the intact animal, in the perfused livers obtained from control and treated rats and in cellular and subcellular preparations obtained from livers of these rats will be performed. In the intact animal, we propose to correlate the dose of ethynyl estradiol and period of treatment required to increase hepatic secreton of very low density lipoprotein triglyceride with serum levels of glucagon and insulin. The glucagon mediated cAMP response of the liver from ethynyl estradiol treated rats is reduced in vitro. Therefore, the interaction of glucagon with ethynyl estradiol will be investigated by several parameters in vivo. We will measure the effect of the infusion of glucagon into the blood of ethynyl estradiol treated rats by monitoring the concentration of cAMP in the liver and serum, and the serum concentrations of glucose, free fatty acids, triglyceride, ketone bodies and insulin. We will investigate the mechanisms by which treatment with estrogen reduces the apparent hepatic synthesis of cAMP in response to glucagon, using the isolated perfused liver. The reduction in synthesis and release of cAMP by livers from ethynyl estradiol treated rats will be correlated with the secretion of triglyceride and production of ketone bodies during infusion of glucagon into the perfusion medium. To study the activity of the adenylate cyclase system at the cellular and subcellular level, hepatocytes, liver slices and plasma membranes prepared from livers of ethynyl estradiol treated rats will be used to achieve these objectives. The proposed studies using in vivo and in vitro experimental protocols, should provide valuable information of how glucagon (a polypeptide hormone) and estrogen (a steroidal hormone) interact to affect cAMP production and thereby modulate hepatic metabolism.